1. 4.4 – Tissues Working Together
A plant leaf is made up of a system of tissues, each with its own specific structure and function.
The primary function of the leaf is photosynthesis where sunlight is used to produce glucose (sugar).
Recall the word equation for photosynthesis is:
chlorophyll
Light energy + carbon dioxide + water glucose + oxygen
Glucose produced during photosynthesis is transferred throughout the plant by the phloem (vascular tissue).

2. Absorbing Light
It is the green pigment chlorophyll that absorbs the light to begin photosynthesis.
Chlorophyll is found in organelles called chloroplasts which are located mostly in the palisade layer and the spongy mesophyll.
Ground tissue (palisade layer and spongy mesophyll) in a leaf is largely responsible for photosynthesis and fills the space between the dermal layers and the vascular tissues.

3. Obtaining Carbon Dioxide
The leaf epidermis contains many tiny openings called stomata, which allow gas exchange and the release of water vapour.
Special dermal cells known as guard cells surround and control each stomata in a leaf.
Most plants have most of their stomata in the lower surface of the leaf to reduce water loss, to provide more surface area for photosynthesis, and to reduce the chance of airborne viruses and bacteria from entering the leaf.

4. Controlling Stomata
When stomata are open, carbon dioxide can enter the leaf and oxygen can escape.
Ideally, plants want to open their stomata whenever it is sunny however, too much water vapour can escape.
Guard cells help the plant to conserve water by altering their shape in response to water levels in the leaf.
The guard cells expand and bend (opening the stomata) when water levels are high.
If there is a shortage of water, the guard cells collapse (closing the stomata).

5. Comparing Plant and Animal Systems
Both animal and plant cells use sugar and oxygen in the process of respiration.
Animals and plants both possess systems that must work together to accomplish complex tasks.
Vascular bundles in plants are similar to veins and arteries in animals.
Plants however, have no organ equivalent to a heart.

6. A Comparison of Animal and Plant Tissue Systems
Task
Animal Organ System
Plant Tissue System
Obtaining food and transporting
The nervous and musculo-skeletal systems are involved with obtaining food
The digestive system processes food
In the Circulatory system, blood vessels transport all digested food nutrients
The entry of necessary carbon dioxide is controlled by cells in the dermal tissue system
The ground tissue system in leaves produces the plants own food (sugars)
The vascular system transports sugars and other complex compounds in phloem

7. Obtaining Water
Leaves reduce water loss with a waxy cuticle and by closing their stomata when water levels are low.
Water enters the plant through the roots and is transport through the xylem from the roots, up the stem, and to the leaves.